1. Field of the Invention
The present invention relates to a protection circuit of a T8 LED (Light-Emitting Diode) lighting tube, and in particular to a circuit that achieves protection of a light source load of a T8 LED tube through at least two rectification circuits that are composed of rectifier semiconductors to realize a function of preventing a reverse flow of electrical current.
2. The Related Arts
A T8 LED (Light-Emitting Diode) lighting tube is commonly used in T8 lighting facilities to serve as a replacement light source for traditional fluorescent tubes. The T8 LED lighting tubes, although helpful in reducing power consumption, are of long-existing apparent drawbacks regarding connection with power supply. For example, as shown in FIG. 1 of the attached drawings, a conventional T8 LED tube 1 has two opposite ends each forming a connector 2. Each connector 2 comprises two conductive pins 3 for removable and electrical engagement with a corresponding connector 5 of a T8 fluorescent light fixture 4 to establish electrical connection of the pins 3 with an alternating current power source P of a T8 fluorescent light fixture 4, so that alternating current from for example electric main can be supplied to light the T8 LED tube 1.
A conventional fluorescent tube receives alternating current is a polarity free manner, meaning the two pins of the fluorescent tube are of no difference from each other; yet this is not the case of light-emitting diodes. In order to make a T8 LED tube connectable to a T8 light fixture in the same polarity free manner as the conventional fluorescent tubes, meaning the two pins 3 of the two connectors 2 of the T8 LED tube 1 are allowed to be arbitrarily mounted to any one of the fixture connectors 5 of the light fixture, a commonly used solution is to short the two pins 3 of each tube connector 2. This makes the pins 3 of the two tube connectors 2 connecting in parallel to a starter 6 of the T8 fluorescent light fixture 4. Consequently, the starter 6 will be enabled when alternating current flows from an electric main to the T8 fluorescent light fixture 4. The starter 6 generates a high voltage surge that is transmitted through the pins 3 of the tube connectors 2 to T8 LED tube 1. Since the T8 LED tube 1 is not designed to operate in the same way as a fluorescent tube that requires preheating to excite ionization of inert gas to induce electric discharge for emission of light, the high voltage surge will damage the T8 LED tube 1 and leads to deterioration of performance and lifespan of components of the LED lighting.
A known solution for the problem of damage of the T8 LED tube 1 caused by the high voltage surge generated by the enablement of the starter of the T8 fluorescent light fixture 4 is to remove the starter 6 from the fluorescent light fixture 4. This solution is impractical in that a user often forgets to remove the starter after replacing the fluorescent tube with an LED tube and eventually leads to undesired damage of the LED lighting tube 1. Further, if the starter is correctly removed from a fluorescent light fixture for installation of an LED tube, there is more trouble that the starter must be re-installed in case the LED tube is to be removed and a fluorescent tube is to be used again. This is certainly troublesome and cumbersome. Another feasible solution is to install a device that suppresses or eliminates surge in the T8 LED tube 1. This, apparently, adds expenses to the manufacturing costs of the T8 LED tubes, making it economically impractical and thus of no industrial value.
References of prior art are known, such as Taiwan Utility Model M368749, which discloses an LED lighting fixture, wherein one or two sets of bridge rectifiers are connected between two first power input terminals or second power input terminals of an end cap of the same side, in order to eliminate the risk of burning out due to incorrect connection when two or more LED lighting fixture are connected in serial. However, no isolation or disablement is realized on the starter of the fluorescent light, fixture. The connection between the first or second power input terminals and an alternating current power supply of the fluorescent light tube shown in the prior art LED lighting fixture indicates that the starter of the fluorescent light fixture will be enabled and put into operation in order to supply the alternating current for operation of the first and second bridge rectifiers. This causes the same problem discussed above that the T8 LED tube 1 is susceptible to damage caused by high voltage surge induced by the operation of the starter, leading to deterioration of performance and lifespan of the components of the LED lighting fixture.